1. Field of the Invention
The present invention relates to a method for the autonomous determination of an inertial positional reference on board a guided projectile through the ascertaining and evaluating of pressure values in the surroundings of the projectile during the movement thereof along a ballistic trajectory. Moreover, the invention relates to an arrangement for the autonomous determination of an inertial positional reference on board a guided projectile which is launched in a ballistic trajectory through measuring of the pressure in the surroundings about the projectile.
2. Discussion of the Prior Art
Measures of the type which are under consideration herein, are essentially known from the disclosure of U.S. Pat. No. 4,606,514, which is jointly assigned to the common assignee of the present application and to the Martin-Marietta Corporation, Bethesda, Md. In that instance, the measurement of the pressure is implemented for the determination of the passage of the projectile through the apogee of the ballistic trajectory; in effect, through determining the timewise sequence of the first derivation in time of the altitude-dependent pressure detonation, which becomes zero during passing through the apogee. Inasmuch as, because of the ballistic conditions, the longitudinal axis of the projectile is oriented in a good approximation in parallel with the spatial horizontal during passage through the apogee, then through the determination of the point in time of the apogee there is determined a pitch position reference angle (namely, zero degrees) along the ballistic trajectory, which can be rendered available to the automatic pilot as an inertial reference for changing the projectile from the ballistic firing or launch trajectory into an extended target searching-gliding trajectory. Due to this autonomous on-board determination of a pitch position-reference angle, there is obviated the need, prior to the firing of the projectile from a weapon barrel or launch tube, to manually enter the starting conditions which determine the ballistic trajectory (namely, with respect to the elevation of the firing barrel or launch tube relative to the horizontal and with respect to the muzzle exit velocity dependent upon the firing charge), which especially under combat field conditions would lead to excessively error-susceptible handicaps in calculating the trajectory.
However, while the determination of the pitch position reference through the intermediary of the autonomous apogee determination on board the projectile has been ascertained is being basically operationally reliable, dependable, it is subject to the disadvantage, that the firing or launch-fixed altimeters which are necessary for the determination of the altitude zero-passage of the trajectory, are relatively imprecise. Resulting therefrom is an area of uncertainty in the timewise and positional determination of the apogee, which becomes more widespread the flatter the ballistic starting trajectory, in effect, the less distinct is the apogee of the trajectory. This uncertainty in the transmission of the information over the apogee to the automatic pilots can have the consequence in the latter, that the preprogrammed point in change for the transition from the ballistic starting flight path into the inclined gliding path can actually be only imprecisely implemented, which corresponds to an imprecision in the delivery of a projectile which is self-guiding and target-seeking during the final flight phase; in essence, adversely influences the effectiveness of the ammunition.